CMP is a popular technique in contemporary integrated circuit processing, for a number of reasons including reduced depth of field in lithography and reduced tolerances in etching. Those skilled in the art are aware of a recurring problem in CMP—that of polishing surfaces that are not uniform.
The polishing rate depends on the loading—the amount of material to be removed per unit area. A solid area will polish more slowly than a sparsely populated area that has projecting areas to be polished on only a small fraction of the total area. The problem is that the sparsely populated areas can be overpolished, resulting to damage to the layer beneath the layer being removed.
An approach that has been used in the art is applying a block etch to the area with the higher loading. This approach often cannot be applied if the topography in the higher loaded area is such that a block etch would damage the structure below the layer being polished.
This problem becomes more acute as layers become thinner and as tolerances become smaller.